Most electronic devices include various rigid components—processors, memories, optical transmitters and receivers, amplifiers, analog-to-digital converters and signal modulators are but a few examples—coupled together, either directly or indirectly by virtue of all being connected to a rigid substrate such as a printed circuit board. Flexible circuits (also commonly known as “flex circuits”) have emerged as a good way to connect certain types of components to a printed circuit board. Flex circuits usually consist of some sort of flexible substrate having with one or more lines of conductive material leading from contact pads at one end of the flex circuit to a corresponding set of contact pads at the other.
Flex circuit offers various advantages. Because it is flexible, it de-couples mechanical stresses so that loads applied to one component are not transmitted to other components. Its flexibility also allows for much more variation in manufacturing tolerances, since the flex circuit can bend to accommodate tolerances that deviate, even significantly, from design dimensions. Finally, flex circuits allow the design of many different form factors that might not be possible if rigid connections to the printed circuit board were needed.
Despite their numerous advantages, however, flex circuits have one important disadvantage: they are hard to attach to a printed circuit board. One current way of attaching flex circuit to a printed circuit board is hot-bar soldering. In hot-bar soldering, the contact pads on one end of the flex circuit are aligned and put in contact with corresponding contact pads on the printed circuit board. A hot soldering bar is then lowered onto the contact pads, thus soldering the pads on the flex circuit to the pads on the printed circuit board. Hot-bar soldering has several disadvantages. Most important, it is hard to reverse and damages the flexible substrate of the flex circuit. Thus, if a flex circuit is incorrectly attached to a printed circuit board and needs to be removed, the device to which the flex circuit is attached may be rendered useless because of solder damage to the flex circuit. This can be a serious problem where the device is sensitive or very expensive.